1. Field of the Invention
The present invention is directed generally to electron beam position control circuitry associated with cathode-ray tubes and, more particularly, to an arrangement wherein the vertical position of one or more scanning electron beams in a color display CRT is accurately controlled to maintain the beam (or beams) along a predetermined scanning path on a color phosphor.
2. Background Information
An arrangement for correcting the scanning position of multiple electron beams in a color television display tube is disclosed in U.S. Pat. No. 3,383,547 issued May 14, 1968. In the '547 patent, a number of sets of red, green and blue phosphor bars, wherein each set is separated by a conducting strip, are arranged on the face of a television receiving tube. In the tube, five collimated electron beams are produced for scanning of the tube, wherein the two outer electron beams are set to track along corresponding ones of the conducting strips, while the three inner electron beams scan a respective one of the red, green and blue phosphor bars. A modulation signal is imposed on one of the outer beams, and a corresponding signal of opposite phase is imposed on the other one of the outer beams. Accordingly, when the two outer beams each strike a conducting strip, no resultant signal is detected at a common conducting strip electrode. Should the collimated beams deviate from the desired scanning paths, an imbalance is detected with respect to the degree to which the two outer electron beams impinge on conducting strips, and a correction signal is applied to a vertical deflection circuit associated with the tube.
Other known arrangements wherein conductive strips or gratings are formed on the inner surface of a CRT face plate are shown in U.S. Pat. No. 2,739,260 issued Mar. 20, 1956, and U.S. Pat. No. 3,569,760 issued Mar. 9, 1971. A system wherein the instantaneous position of an electron beam is obtained during each horizontal line scan by the use of a series of vertically aligned conductive strips, is disclosed in an article entitled "An Electron Beam Indexing Colour Display System" by J. A. Turner, in Displays (British) (October 1979). All of these systems, however, are directed primarily to arrangements for enabling a single electron beam to produce a color television picture of suitable quality, and are not concerned with the vertical positional alignment of one or more electron beams during scanning in a cathode-ray tube.